1. Field of the Invention
The present invention relates to the BaTiO3—PbTiO3 series single crystal that can be utilized as a piezoelectric element, for example, and also, relates to the method of manufacturing the same. Further, the invention relates to a piezoelectric type actuator formed by the BaTiO3—PbTiO3 series single crystal, and the liquid discharge head that uses such piezoelectric type actuator as well.
2. Related Background Art
The BaTiO3 series single crystal is a nonlinear optical crystal utilized for optical communications, information processing, or the like, and having a great marketability, which is not only used as a phase conjugate wave generating medium for a high resolution image processing, a real-time hologram, or a laser resonator, but also, used as a highly capable piezoelectric material if the crystallization thereof can be implemented at lower costs.
Now, obviously, the composition of the BaTiO3 makes it difficult to obtain single crystal directly from the BaTiO3 solution when BaTiO3 series single crystal is manufactured. Therefore, only the flux growth that uses solution (flux) having fluoride and chloride as main component or the method, in which the BaTiO3 series single crystal of low-temperature component is picked up directly by making the composition of the solution TiO2 rich (the so-called top seeded solution growth (TSSG method)), is applicable to the growth thereof. With the flux growth, the obtainable size is only 1 mm3 or less approximately. Also, for the TSSG method, not only an expensive noble metal crucible, such as a platinum crucible, is needed, but the growing speed is slow to make the manufacturing costs extremely high.
Conventionally, it has been attempted to provide a method for manufacturing larger BaTiO3 series single crystal more effectively and easily with the improvement of the aspects that present the problems as described above.
For example, there are experiments carried out in manufacturing BaTiO3 series single crystal efficiently by sintering method. In the specifications of Japanese Patent Application Laid-Open Nos. 4-300296, 5-155696 and 5-155697, a method for manufacturing BaTiO3 series single crystal is disclosed, in which the BaTiO3 series single crystal serving as the seed crystal is coupled with the BaTiO3 polycrystal, and heated to mono-crystallize such polycrystal by means of solid-phase reaction. In the specification of Japanese Patent Application Laid-Open No. 9-263496, a method for manufacturing BaTiO3 series single crystal is disclosed, in which a temperature gradient is given to the BaTiO3 micro-crystal granular aggregate, the mol ratio of Ti/Ba of which is 1.0 or more and 1.1 or less, for the execution of single crystallization thereof. With these methods, however, the mono-crystalline growth rate greatly varies to make it impossible to grow any bulky single crystal with good reproducibility. Also, the rearrangement density is high, and the crystallinity of the BaTiO3 series single crystal thus obtained is inferior to the one obtained by the conventional TSSG method and the flux method. There are also the examples of solid-phase methods other than the sintering method. In the specification of Japanese Patent Application Laid-Open No. 59-3091, there is the disclosure of a method for manufacturing the oxide single crystal, in which a crystal oxide, such as PbTiO3, BaTiO3, SrTiO3, CaTiO3, is quenched and solidified after molten to make it amorphous, and then, re-crystallized under a temperature gradient. This method makes the manufacturing apparatus and process complicated, because there is a need for a process to melt the crystal oxide. Also, the single crystal thus obtained has inferior crystallization properties, and only the crystal that has a high ratio of pore content is obtainable eventually.
Also, improvement studies have been made on the TSSG method and the flux method. In the specification of Japanese Patent Application Laid-Open No. 6-321698, there is disclosed, as the flux method, a method for manufacturing BaTiO3 using a mixed substance of BaF2, NaF, Li2MoO4, or the like as flux. In this method, the solubility of BaTiO3 is enhanced for the purpose of obtaining bulky BaTiO3 series single crystal with a long-time crystal growth. However, this method is not fully satisfactory in terms of the time required for manufacturing and costs. In the specification of Japanese Patent Application Laid-Open No. 9-59096, there is disclosed BaTiO3 series single crystal having the doping of fine quantities of Mg and Fe. This material aims at obtaining a high photo-refractivity in the near infrared range, but Mg, Fe, or some other element, which may exert unfavorable influence on the piezoelectric property, is contained in that material. As a result, it is not preferable to use this as a piezoelectric material. Also, for the utilization at the industrial level, it is not satisfactory in terms of the time required for manufacture and costs.
As described above, the TSSG or flux method for manufacturing BaTiO3 series single crystal makes it extremely difficult to improve problems related to manufacturing efficiency, such as the time required for manufacturing and costs, among some others. Here, although the sintering method is anticipated to enhance the manufacturing efficiency, the variation of growing speed of BaTiO3 series single crystal makes it impossible to obtain any satisfactory result, and also, the crystallinity of the BaTiO3 series single crystal thus obtained is inferior to the one obtainable by means of TSSG or flux method. In other words, it has been difficult to implement the manufacture of BaTiO3 series single crystal having excellent crystallinity and property in a shorter period of time at lower costs.